Today, fuel filters can be found in any motor vehicle and serve for filtering out different kinds of contaminations such as, for example, solid particles, water, etc. from the fuel to be combusted before entering an internal combustion engine. Particular attention is recently being paid to filtering out water from the fuel to be combusted because water portions in the fuel can result in corrosion and an impairment of the engine performance and because the water content in particular in modern biofuels such as, for example, biodiesel, is significantly higher than in known fossil fuels. The reason for the high water content in biofuels is in particular that the latter are highly hygroscopic. For this reason it is known to combine fuel filters with so-called water separators in order to achieve in this manner that the internal combustion engine is supplied with fuel that is as pure as possible. The separated water is collected in suitable water collection chambers of the water separator and is periodically discharged or discharged as needed. In addition, an activated carbon filter can be integrated in a discharge line of the water separator, which activated carbon filter absorbs the carbon portions still remaining in the water to be discharged and thus prevents that the same escape unintentionally into the environment.